In recent years, an imaging apparatus provided with an auto focus (AF) function for automatically adjusting the focus during imaging is widely used. The AF systems are roughly classified into an active system and a passive system. In the active system, the time of return of a reflected wave, such as infrared light and ultrasound, applied to an object (subject) and the illumination angle are used to detect the distance. In the passive system, an image captured by a lens is used to measure the distance. There are a contrast detection system and a phase difference detection system in the passive system.
Examples of the phase difference detection system include: a system provided with an image sensor dedicated to phase difference AF in addition to an image sensor for imaging; and an image plane phase difference AF system in which phase difference detection pixels are incorporated into an imaging sensor. In either system, the light entering from the lens is divided into two (pupil division), and the focus position is detected from the deviation of the images. The former is provided with the image sensor dedicated to the phase difference AF in addition to the image sensor for imaging, and there is a disadvantage that the size of the imaging apparatus becomes large. The latter has an advantage that the size of the imaging apparatus can be small because the pixels for phase difference detection (phase difference detection pixels) are incorporated into the image sensor for imaging.
In the image plane phase difference AF system, an AF operation is performed based on phase difference signals acquired from the phase difference detection signals. A plurality of image plane phase difference pixels are arranged in an angle of view, and the pixels have a pixel structure such that left and right halves or upper and lower halves of openings on photodiodes as light receiving devices are shielded. The image plane phase difference pixels are provided in pairs, in which one half of the subject light is shielded in one image plane phase difference pixel, and the other half of the subject light is shielded in the other image plane phase difference pixel. One phase difference signal is created based on different incident angle characteristics of the image plane phase difference pixels in pairs (for example, see PTL 1).
PTL 1 discloses a light shielding portion of the image plane phase difference pixel formed such that the position of an imaging point of a microlens and the position of an edge portion on an entrance side of the light shielding portion are separated according to the change in the image height. Although the angle of incidence of the subject light entering the image sensor is gradually deviated from the imaging point of the microlens outside of the axis of the set lens, the technique of PTL 1 can be applied to design the position of the end portion on the entrance side of the light shielding portion in line with the angle of incidence of the subject light from the set lens according to the coordinates in the chip.